Abstract

In this paper, 14.5 yr of JPL timing data are analyzed to study the
spindown of the Vela pulsar. Discontinuities in the spin frequency and
its derivatives have bimodal amplitude distributions. Macrojumps are
characterized by relative changes in spin rate of about 10 to the -6th
with a derivative of 0.01, while microjumps have relative changes in
spin rate of less than about 10 to the -9th with derivative of less than
about 0.0001. Macrojumps display a (+,-) signature with a well-defined
ratio of the amplitudes. Microjumps, however, show all possible signs of
events and a larger range in signature. Six macrojumps and their
associated transients are quantified using a 10-parameter model for each
jump. Amplitude and decay time parameters vary by a factor of about five
over the set of jumps. The results are discussed in terms of superfluid
vortex models. The macrojumps are consistent with a model in which
angular momentum is suddenly transferred to the crust from a more
rapidly rotating superfluid core, followed by relaxation of the
spin-down rate.